Buildings, automobiles, vacuum cleaners, air purifiers, air conditioning systems and fluid filtering systems are equipped on their interior with a filter for filtering out all types of foreign particles, such as dust, which are contained in the air or the fluid that is fed in.
Such filters are ordinarily made of non-woven fabric with zigzag-type pleats.
In reference to one such filter, U.S. Pat. No. 7,503,954, filed and registered by the above applicants, proposes a “filter element”; said patent relates specifically to a filter element made of non-woven fabric, wherein the filter element comprises a “filter web” that is pleated in a zigzag manner, which is inserted into a holder such as a filter frame and/or a filter housing having a flat wall in at least one end position, said filter element having at least one front end face, viewed in the direction of the pleats, with the front end face corresponding to the flat wall of the holder, and as a consequence, the filter element has the advantage that the front end face of the filter element is curved outward in a convex manner, and the material of the filter web being selected such that the filter web can be inserted into the holder without corrugation, with the filter web firmly contacting the end wall of the holder as a result of elastic pre-tension, and/or the front end face being “conditioned”.
However, with conventional filters, including that of U.S. Pat. No. 7,503,954, the problem exists that after a certain amount of time, foreign particles such as dust, etc. can collect on the surface of the side along which the air flow is fed, and as a result, the openings in the filter become clogged and filtration efficiency deteriorates, and liquid foreign particles or solid foreign particles that have been deposited in the filter decompose, resulting in contamination or odors in the filtered air flow.
Moreover, U.S. Pat. No. 6,894,620, filed and registered by the above applicants, proposes a “method and device for monitoring the service life of a filter”, specifically a filter in a filtering device installed in a fan, in particular, a method for monitoring the service life of a filter in the air conditioning system of an automobile; in this case, said filters are preferably designed such that whenever the device is in operation, the actual air speed in the bottom region of the filter is measured by a sensor, compared with the normal air speed of the filter when not in use, and transmitted to the service device and/or displayed on the display device, and, if the predetermined threshold value or threshold range of the actual air speed is not reached, a signal indicating that the filter should be replaced is emitted.
The problem exists, however, that as the filter is being used, a gap can form between the edge of the filter and the filtering device in which the filter is installed, and this gap can result in a change in the air flow, and, because in conventional filtering devices a sensor measures the change in the air flow resulting from this gap, measurement errors occur, and as a result, the sensor is unable to measure the replacement interval for the filter.